Fluidic demodulator

ABSTRACT

A fluidic device to demodulate a fluidic AC carrier signal to obtain a pure fluid signal. A modulated signal is impressed through an orifice to a cavity resonator. The output of the resonator is an orifice of smaller dimensions than the input orifice. Between limited frequency ranges the resonator will successfully demodulate AM and FM signals. If another orifice is placed in between the input and output orifices and opened to ambient pressure, the device will successfully demodulate FM and AM signals again within different but still limited frequency ranges.

United States Patent [72] lnventors Jonathan E. Fine Washington, D.C.';

Carl J. Campagnuolo, Chevy Chase, Md. [2]] Appl. No. 734,064 [22] Filed June 3, 1968 [45] Patented Feb. 9, 1971 [73] Assignee the United States of America as represented by the Secretary of the Army [54] FLUIDIC DEMODULATOR 2 Claims, 6 Drawing Figs.

[52] U.S.Cl 137/1, 137/81.5 [51] 1nt.Cl F15c1/04 [50] Field of Search 137/81.5

[56] References Cited UNITED STATES PATENTS 3,185,166 5/1965 Hortonetal 137/81.5 3,228,410 1/1966 Warren et a1. 137/81.5 3,398,758 8/1968 Unfried 137/81.5 3,432,804 3/1969 Beeken 137/81.5X

3,434,487 3/1969 Bauer 137/81.5 3,401,710 9/1968 Keto 137/81.5 3,461,895 8/1969 Colston 137/31.5 3,465,775 9/1969 Rose l37/81.5 3,469,593 9/1969 O'Keefe 137/81.5' 3,451,269 6/1969 Johnson 137/81.5X 3,503,408 3/1970 Metzger 137/81.5 3,505,880 4/1970 Riordan 137/81.5X

Primary Examiner-Samuel Scott Attorneys-Harry M. Saragovitz, Edward J. Kelly, Herbert Ber] and John D. Edgerton PATENTEU FEB s .97.

SHEET 2 OF 2 o A 1 v l/5//, A] A) j I x I v W Fm,

INVENTOHS JONATHAN E. FINE CARL J. CAMPAGNUOLO MM ,19, M

XTTO NEYS FLUIDIC DEMODULATOR RIGHTS OF GOVERNMENT The invention described herein may be manufactured, used and licensed by or for the United States Government for governmental purposes without the payment to us of any royalty thereon.

BACKGROUND OF THE INVENTION The science of fluidies, or the control of fluids with no moving parts, has furnished a means of signal processing which is more rugged, and less liable to damage from environmental changes of acceleration, vibration, radiation and temperature, than their electrical and mechanical counterparts.

A limitation on current state of the art in fluid proportional amplifiers is noise. The high noise level in proportional amplifiers limits their usefulness in amplifying small signals and for this reason it becomes expedient in fluidics, as in electronics, to resort to carrier systems. In such systems the signal to be amplified is impressed on a carrier signal which is out of the noise range of the amplifier. The modulated carrier is then amplified and fed into the demodulator, which removes the carrier signal and produces an amplified replica of the original signal. Carrier systems typically used are amplitude-modulated (AM), frequency-modulated (FM), and pulse-position modulated systems.

The successful use of carrier systems depends upon the input-output characteristics of the elements in the system and the properties of the paths connecting them. The most faithful reproduction will take place if the output signal characteristic of each component is a linear function of the input signal characteristic, at least over the useful input signal range. Specifically, the instantaneous output flow of an AM demodulator must be a linear function of the input amplitude and the instantaneous output flow of an FM demodulator must be a linear function of the input frequency.

It is therefore an object of this invention to provide a fluidic demodulator which will demodulate a fluidic AC carrier signal and obtain a pure fluid signal useful in control or readout systems.

An additional object of this invention is to provide a means of demodulating an electrical signal in an electrofluidic control system by applying existing electrical and radio techniques to fluid amplifiers.

STill another object of the invention is to provide a fluidic demodulator which will produce a demodulated output signal that is a linear function of the modulated input signal.

SUMMARY OF THE INVENTION The demodulator herein described uses the flow-frequency and flow-amplitude characteristics of cavities and tubes operating near either of two resonant conditions to permit an AM or FM carrier signal to be demodulated to give a unidirectional flow useful in readout or control of other fluid elements.

BRIEF DESCRIPTION OF THE DRAWINGS The specific nature of the invention as well as other objects, aspects, uses, and advantages thereof, will clearly appear from the following description and from the accompanying drawing, in which:

FIG. 1 shows a fluidic demodulator in accordance with my invention.

FIGS. 2A, 2B and 2C illustrate the operation of the fluidic demodulator of FIG. 1.

FIG. 3 is an illustration used to explain the operation of another embodiment of my invention.

FIG. 4 shows another embodiment of my invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a cavity resonator demodulator in accordance with my invention which operates on the principle of momentum rectification taking place at a small orifice at one end of the resonating cavity or tube. The demodulator 10 has a resonant cavity 14, an input orifice l3 and an output orifice 15. The cavity chamber 14 and the orifices l3 and 15 can be made of any suitable material having the structural properties necessary to withstand the fluid pressures present during operation.

Operation of the cavity resonant modulator can be more readily understood by referring to FIGS. 2A, 2B and 2C. When the modulated fluid wave is applied to the input orifice 13 in FIG. 1 the oscillating pressure field at the output side of the cavity 14 drives the fluid in and out of the orifice 15 as a solid piston, shown as 20 in FIG. 2A. During the half cycle when the fluid piston is moving outward (FIG. 2B), it accelerates the fluid ahead of it as shown by arrows 21. In FIG. 2C this fluid continues in motion 27 even after the fluid piston 20 reverses its direction, thereby creating a low-pressure region near the orifice 15 axis. Ambient fluid from all directions will then fill the lower pressure region as shown by arrows 23. The resulting flow along the axis is therefore a pulsating DC flow whose amplitude at a given axial station depends upon the frequency and pressure amplitude across the orifice 15.

If, for a particular cavity resonator and input and output orifices, a graph were made of the output flow from the cavity as a function of driver frequency for a fixed pressure amplitude, it would be seen that the graph would be linear in a defined range of frequencies, thus showing that the cavity resonator could be used as an FM demodulator in these ranges.

Similarly if the velocity from the output were plotted as a function of pressure amplitude for a fixed driving frequency, it would be found that the curve is linear for a limited range of amplitudes thus showing that the device could be used for AM demodulation in this amplitude range.

It is known from the literature that standing waves in air set up in a tube of circular cross section generate a symmetric system of steady vortexes in which the flow direction is from flow loops (antinodes) to flow nodes along the wall and from flow nodes to the How loops along the axis. Such a pattern of standing waves was described by Lord Rayleigh (see Collected Papers, Vol. 2, page 239, 1900) and is shown in FIG. 3. An open end of a tube corresponds to a blow loop. Therefore as shown in FIG. 3, the flow 30 tends to enter the open end 31 along the wall and leave along the axis. The resulting velocity profile curve 32 is sketched in the FIG. at the open end 31. The areas 36 and 38 are shaded and represent the flow into the open end 31. The crosshatched area 34 represents the flow out of the open end 31. In the case of a tube with one end open, the two areas must be equal in order to conserve mass. Addition of the second opening 40 in FIG. 3 permits mass to be conserved while causing a net flow through the tube.

The size and shape of the opening; 40 causes the velocity profile 41 at a given frequency to have greater darkened areas 45 and 46 than crosshatched area 43, thus indicating a net flow into the opening 40. At open end 31 the crosshatched area 32 is larger than the darkened areas 36 and 38 thus indicating the net flow out of the tube. Because mass must be conserved the sum of the shaded areas of both profiles must be equal to the sum of the crosshatched areas, insuring that the net flow into the tube equals the net flow out. The direction of the mass transfer in the tube can be reversed by suitably adjusting the frequency and/or intensity of the fluidic waves so that the profiles at openings 31 and 40 are interchanged.

FIG. 4 shows another embodiment of a resonant cavity demodulator in accordance with my invention utilizing the concept of generation of net flow in a circular tube by Rayleigh circulation. The demodulator 50 of FIG. 4 uses a circular tube 53 with a resonator section 51 and having orifices 45 and 30. Orifice 30 opens up to ambient pressure at 32 and orifice 45 is the output orifice from which the demodulated signal is obtained. The distance from the axis of orifice 30 to the output orifice 45 is 2 where n is a small integer and A is the wavelength. The open end 47 ofthe tube 53 is connected to or is part ofa fluid transmission line which brings the modulated signal into the resonator section 51 of the tube. The actual dimensions of the resonator section 51 are determined after an equivalent circuit is derived for the transmission lines section of the tube 53.

As with the preceding embodiment of my invention if the velocity out of orifice 45 were plotted as a function of the pressure amplitude for a driving frequency, it would be apparent that the curve is fairly linear for defined amplitude range and the device could be used for AM demodulation in this amplitude range. Similarly, plotting flow output as a function of frequency for a fixed amplitude pressure signal at orifice would define the linear range where the device could be used for FM demodulation.

It should be realized that the pressure input to both of my embodiments disclosed may be a pure fluid-modulated carrier or the field set up by an electrically driven piston or diaphragm. Where the input pressure signal is generated by an electrically driven diaphragm, it then becomes possible to demodulate an electrically modulated AM or FM signal.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of the invention as defined in the appended claims.

We claim:

1. A passage fluidic demodulator for removing the carrier signal and transmitting an amplified replica of the original signal comprising:

a. a substantially cylindrical resonant cavity for receiving a fluid pressure signal;

b. an input orifice located at one end of said cavity for transmitting said fluid pressure signal into said cavity;

c. an output orifice located at the opposite end of said cavity for transmitting a fluid flow signal out of said cavity. the area of said output orifice being substantially smaller than the area of said input orifice; and

d. an auxiliary orifice for entraining ambient flow, said auxiliary orifice located along the cylindrical surface and at a distance NA from said output orifice, wherein A is the wavelength of the input signal and n isa small integer.

2. A passive method of demodulating an acoustic signal comprising the steps of:

a. transmitting an acoustic signal having a carrier signal frequency and a modulating signal frequency through an input orifice of a resonant cavity, said resonant cavity being responsive to frequencies of the modulating signal and being nonresponsive to the frequencies of the carrier signal; a I

b. producing resonance in said resonant cavity, said resonance being within the range of frequencies of said modulating signal;

c. entraining ambient flow through an auxiliary orifice located at a distance of from said output orifice, wherein A is the wavelength of the acoustic signal and n is a small integer;

d. transmitting a pressure signal through an output orifice of said resonant cavity, said output orifice being substantially smaller in area than said input orifice; and

e. measuring the output flow of said pressure signal,

whereby said output flow of said pressure signal is proportional to the modulating signal of said acoustic source. 

2. A passive method of demodulating an acoustic signal comprising the steps of: a. transmitting an acoustic signal having a carrier signal frequency and a modulating signal frequency through an input orifice of a resonant cavity, said resonant cavity being responsive to frequencies of the modulating signal and being nonresponsive to the frequencies of the carriEr signal; b. producing resonance in said resonant cavity, said resonance being within the range of frequencies of said modulating signal; c. entraining ambient flow through an auxiliary orifice located at a distance of n from said output orifice, wherein lambda is the wavelength of the acoustic signal and n is a small integer; d. transmitting a pressure signal through an output orifice of said resonant cavity, said output orifice being substantially smaller in area than said input orifice; and e. measuring the output flow of said pressure signal, whereby said output flow of said pressure signal is proportional to the modulating signal of said acoustic source. 